This invention relates to the solidification of liquids containing sodium, nitrate and chloride ions by calcining the liquid in a fluidized-bed calciner. More particularly, the invention relates to the solidification of liquid radioactive wastes for long-term storage as a solid. Specifically, the invention is directed towards minimizing the volatilization of the chlorides present in the liquid during the solidification process.
Liquid radioactive wastes produced during the reprocessing of spent nuclear reactor fuel elements to recover the unburned nuclear fuel material are more conveniently, safely and economically stored for long periods of time as a solid. Consequently, methods have been sought for converting the liquid radioactive waste to solids for long-term storage. One technique which has proven to be particularly adaptable to the solidification of liquid radioactive waste is calcination in a fluidized-bed calciner. Such a fluidized-bed calciner has been successfully operated for a significant period of time at the Waste Calcining Facility of the Idaho Chemical Processing Plant (ICPP) located at the National Reactor Testing Station in southeastern Idaho.
While several types of liquid radioactive waste have been readily calcined and techniques have been developed to permit the calcining of other types of waste in the fluidized-bed calciner, each type of waste gives rise to unique and characteristic problems and special considerations which stem from the particular composition of the waste. Differences in the composition of the various types of waste arise from the various process steps for the recovery of the fuel in which the waste is generated and the various types of fuel and cladding introduced at the head-end of the fuel recovery process.
A typical problem which arises in the fluidized-bed calcining of the many types of waste is the fouling of the fluidized bed by particle agglomeration due to the presence of sodium nitrate. Sodium nitrate does not decompose but melts and exists in a molten state between 305.degree.C. and 833.degree.C. which includes the normal range of calcination temperatures. Therefore it is present in a molten state and can cause agglomeration of the bed particles and consequent fouling of the fluidized bed.
Volatilization of various corrosive components, such as fluorides and chlorides, presents problems downstream from the fluidized bed in the off-gas cleanup system. Consequently, it is desirable to minimize fluoride and chloride volatility. One type of liquid radioactive waste which presents both the problem of fluidized-bed particle agglomeration and chloride corrosion problems is ICPP intermediate-level waste, which is described in more detail below. Approximately 850,000 gallons of intermediate-level radioactive waste are stored in underground storage tanks at the Idaho Chemical Processing Plant. This waste must be solidified in the future to meet with AEC waste-storage specifications and to make room for additional waste generated at the ICPP.
It is an object of the present invention to provide a calcination process for this intermediate-level waste.
It is another object of the present invention to provide a calcination process for the fluidized-bed calcining of the intermediate-level waste in which bed particle agglomeration will not be a problem.
An additional object of the present invention is to provide a method for the fluidized-bed calcining of intermediate-level waste in which the volatilization of chlorides will be minimized.